WHOLE-HOUSE VENTILATION SYSTEMS Improved control of air quality BUILDING TECHNOLOGIES PROGRAM OFFICE OF ENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY Buildings Fact sheet for homeowners and contractors on how to employ Whole-house ventilation in the home for comfort and safety.

PURPOSE OF VENTILATION. All homes need ventilation—the exchange of indoor air with outdoor air—to reduce indoor moisture, odors, and other pollutants. Contaminants such as formaldehyde, volatile organic compounds (VOCs), and radon that may cause health problems can accumulate in poorly ventilated homes. Inadequate ventilation allows unpleasant odors to linger. Excess moisture generated within the home needs to be removed before high humidity levels lead to physical damage to the home or mold growth.

VENTILATION STRATEGIES. To ensure adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) says that the living area of a home should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per minute (cfm) per person, whichever is greater.

Natural ventilation—uncontrolled air movement into a building through cracks and small holes (infiltration) and through vents such as windows and doors—is the traditional method of allowing fresh outdoor air to replace indoor air. Nowadays, because of central heating and cooling, as well as the desire for privacy, people tend to make little use of windows for ventilation, so infiltration has become the principal mode of natural ventilation in homes. Unfortunately, a home’s natural infiltration rate is unpredictable and uncontrollable because it depends on the home’s airtightness, outdoor temperatures, wind, and other factors. During mild weather, some homes may lack sufficient ventilation for pollutant removal. Tightly built homes may have insufficient ventilation at most times. Homes with high infiltration rates may experience high energy costs. Also, infiltration may allow contaminated air to enter from a polluted area such as a garage or crawlspace, or may not ventilate the house uniformly.

WHOLE-HOUSE VENTILATION SYSTEM DESIGNS. The decision to use whole-house ventilation is typically motivated by concern that natural ventilation is not providing adequate air quality, even with source control by spot ventilation. Whole-house ventilation systems are usually classified as exhaust ventilation if the mechanical system forces inside air out of the home, supply ventilation if the mechanical system forces outside air into the home, or balanced ventilation if the mechanical system forces equal quantities of air into and out of the home.

WHOLE-HOUSE VENTILATION SYSTEM DESIGNS
The decision to use whole-house ventilation is typically motivated by concern that natural ventilation is not providing adequate air quality, even with source control by spot ventilation. Whole-house ventilation systems are usually classified as exhaust ventilation if the mechanical system forces inside air out of the home, supply ventilation if the mechanical system forces outside air into the home, or balanced ventilation if the mechanical system forces equal quantities of air into and out of the home.

Exhaust ventilation systems work by depressurizing the building. By reducing the inside air pressure below the outdoor air pressure, they extract indoor air from a house while makeup air infiltrates through leaks in the building shell and through intentional, passive vents.

Supply ventilation systems work by pressurizing the building. They use a fan to force outside air into the building while air leaks out of the building through holes in the shell, bath and range fan ducts, and intentional vents (if any exist).

WHOLE-HOUSE VENTILATION SYSTEMS
the most time, and exhaust air from rooms where moisture and pollutants are most often generated (kitchen, bathrooms, and perhaps the laundry room). Some designs may use a single-point exhaust. Because they directly supply outside air, balanced systems allow the use of filters to remove dust and pollen from outside air before introducing it into the house. Balanced systems are usually more expensive to install and operate than supply or exhaust systems because they require two duct and fan systems. Like these other systems, balanced ventilation systems do not temper or remove moisture from the make-up air before it enters the house and thus may contribute to higher heating and cooling costs compared with heat-recovery systems. Like supply ventilation systems, outdoor air may need to be mixed with indoor air before delivery to avoid cold air drafts in the winter.

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